Roads, parking lots and other surfaces are often paved with material such as a mixture of asphalt and gravel to provide a sealed, durable, traffic-bearing surface. A variety of relatively sophisticated machines and processes are used to apply a “mat” of hot asphalt onto the surface to be paved. Following deposition of the paving material onto the surface, the material is typically compacted with a separate compactor machine to a desired state. In most paving operations, it is desirable to deposit paving material in such a manner that a relatively smooth and uniform surface results. Producing a paved surface to desired specifications can be a relatively challenging process, however, requiring relatively highly skilled paving machine operators, often working in cooperation with other machine operators and technicians. Paving contractors tend to be compensated based at least in part on the quality of the end product. Bonuses are typical for superior work, exceeding specifications; re-work or penalties are not uncommon for nonconforming jobs.
One type of common paving machine consists of a self-propelled machine having a paving material hopper, a material feed system and a “screed.” The screed is typically supported by the machine and trails behind it such that it “floats” on top of freshly deposited asphalt to smooth and compact the same, in preparation for further work by a dedicated compacting machine. One factor which has been discovered to affect the end quality of a paving job relates to deposition of paving material in front of a paving machine screed during operation. In particular, where the paving material is deposited at an inappropriate thickness or “head height” onto the work surface in front of the screed, variations in the smoothness, regularity and overall quality of the asphalt mat can result. Control over the head height of the freshly deposited paving material in front of the screed is conventionally achieved via the use of one or more mechanical contact sensors or one or more sonic sensors which output signals indicative of the paving material head height such that a material feed system of the paving machine may reactively speed up or slow down, by either electronic or operator control.
While utilizing contact sensors has proven more useful than operator guesswork, or visual inspection, a variety of factors can affect the ability of an operator or control system to adequately address changes in material feed demand. As a result, paving operations can create waves in the paved surface corresponding with instances of too great and/or too little paving material head height in front of the screed. Where machine propel speed is increased, for example, a corresponding adjustment in material feed in the paving machine may be necessary. In a conventional reactive system, paving material feed is not increased or decreased to accommodate a change in machine propel speed until after a drop or an increase in head height is detected. Similarly, extension and retraction of a variable width screed can affect the material feed demand in a manner not adequately addressed by reactive material feed control systems. Despite advances in paving strategies, control system sophistication, and machine positioning technology, reactive approaches to changes in material feed demand have been shown to be inadequate, and the many instances of lower quality paving work reflect the shortcomings associated with the conventional state of the art.
One attempt at paving machine design and control that is directed toward improved paving quality is known from U.S. Pat. No. 6,520,715 to Smith (“Smith”). The machine in Smith utilizes a material feed system to deposit a relatively large volume of paving material onto a work surface. Excess paving material is then removed from the large pile of material as the machine travels across a work surface by an adjustable, multi-bladed assembly. Material which is removed by the multiple blades is then returned to a storage bin in anticipation of re-deposition. Smith's machine accounts for variations in paving thickness across a width and longitudinal dimension of the work surface to be paved, via its paring away of material from the pile deposited onto the work surface. While Smith may have advantages in certain environments, the machine is quite complex. Moreover, Smith's approach wherein an excess volume of material is deposited onto a surface, then extra material removed and returned to a hopper for re-deposition, is inherently inefficient.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.